Owing to the king of Edom's refusal to permit Israel to pass through his land, they were obliged, at the very point when they believed themselves at the end of their march, to continue it, so as to go around the land of Edom. The people, weary of the many years' marches, now became peevish, saying: "We had already been close to the promised land, and now must turn about once more! It was the same with our fathers who, close to their goal, had to turn back and roam about for thirty-eight years. Thus will it be with us!"  In their dejection they set about murmuring against God and Moses, "master and servant being to them as one." They complained that they were entirely thrown upon manna as a means of sustenance. This last mentioned complaint came from those in regard to whom God had vowed that they should never see the land which He had sworn unto the Patriarchs. These people could not bear the sight of the products of Palestine's soil, dying as soon as they beheld them. Now that they had arrived at the outskirts of the promised land, the merchants brought into the camp of the Israelites the native products, but these, unable to partake of them, still had to continue to gather sustenance exclusively from manna. 
Then a voice sounding from the heavens became audible upon earth, making this announcement: "Come hither and behold, O ye men! Come hither and hearken, ye the serpent with the words, 'Dust shalt thou eat,' yet it complained not of its food. But ye, My people that I have led out of Egypt, for whom I caused manna to rain down from heaven, and quails to fly from the sea, and a spring to gush forth from the abyss, ye do murmur against Me on account of manna, saying, 'Our soul loatheth this light bread.' Let now the serpents come, that complained not, even though whatever food they ate tasted only of the dust, and let them bite those who murmur though they have a food that possesses every conceivable flavor.  The serpent, which was the first creature to slander its Maker and was therefore punished, shall now punish this people, which, not profiting by the example of the serpent's punishment, blasphemes its Creator by declaring that the heavenly food that He sends them would finally bring them death." The very serpents that during the forty years' march had been burned by the cloud of glory and lay heaped up high round about the camp, these same serpents now bit the people so terribly that their poison burned the souls of those whom they attacked. 
When Moses betook himself to those who had been bitten, hearing that they were too ill to come to him,  they, conscious of their guilt, said to him: "We have sinned, because we have spoken against the Lord and against thee; pray unto the Lord, that He take away the serpents from us." Such was the meekness of Moses, that he instantly forgave the people's transgression in regard to himself, and at once implored God's aid. God also, however, forgave their sin as soon as they had shown penitence, and thus set an example to man likewise to grant forgiveness when it is requested.
As a healing for those who had been bitten, God now bade Moses to make a serpent of brass, and put it upon a pole, that it might come to pass that every one who was bitten might look upon it and live. Moses did as he was bidden, and made a serpent of brass. As soon as he hurled it on high, it remained floating in the air, so that all might be able to look upon it.  He mad the serpent brass, because in Hebrew Nahash signifies "snake" and Nehoshet, "brass"; hence Moses made the serpent of a substance that had a sound similar to that of the object fashioned out of it.  It was not, however, the sight of the serpent of brass that brought with it healing and life; but whenever those who had been bitten by the serpents raised their eyes upward and subordinated their hearts to the will of the heavenly Father, they were healed; if they gave no thought to God, they perished. 
Looking upon the serpent of brass brought about healing not only to those who had been bitten by serpents, but also to those who had been bitten by dogs or other animals. The cure of the latter was effected even more quickly than that of the former, for a casual glance sufficed for them, whereas the former were healed only after a long and insistent gaze.